I've swam competitively for the past fifteen years and the most important thing to remember especially in these longer races is long smooth strokes and plenty of breathing. If you are choppy that is wasted energy, pretty over power is always the way to go especially when you aren't a strong swimmer Is it an open water swim or is it in a pool? If its in a pool use the walls to your advantage and push off of them hard don't waste a wall by just touching and going you need to explode off of the wall. If it is open water make sure your stroke is long and pick a side you are comfortable breathing to and breathe to that side the whole race(this can be done in a pool as well). All that extra breathing helps prevent lactic acid build up and it helps you get into a good rhythm. Hope this helps. Don't panic pick a pace you are comfortable with because going too fast can kill the race bad. Good luck!